1. Field
The present invention relates generally to equalization in communications systems, and more specifically, to a universal receiver incorporating a RAKE receiver and a hybrid equalizer.
2. Background
Communications systems are used for transmission of information from one device to another. Prior to transmission, information is encoded into a format suitable for transmission over a communication channel. The transmitted signal is distorted as it travels through the communication channel; the signal also experiences degradation from noise and interference picked up during transmission. An example of interference commonly encountered in band-limited channels is called inter-symbol interference (ISI). ISI occurs as a result of the spreading of a transmitted symbol pulse due to the dispersive nature of the channel, which results in an overlap of adjacent symbol pulses. The received signal is decoded and translated into the original pre-encoded form. Both the transmitter and receiver are designed to minimize the effects of channel imperfections and interference. For the purposes of this disclosure, interference or distortion due to channel imperfections, or any combination thereof will be referred to generally as noise.
Various receiver designs may be implemented to compensate for noise caused by the transmitter and the channel. By way of example, an equalizer is a common choice for dealing with ISI. An equalizer corrects for distortions and generates an estimate of the transmitted symbol. In the wireless environment, equalizers are required to handle time-varying channel conditions. Ideally, the response of the equalizer adjusts to changes in channel characteristics.
Equalizers are generally complex, tending to increase the power consumption of a communication device. A need exists, therefore, for an equalizer design that reduces power consumption. Further, there is a need for controlling an equalizer so as to operate the equalizer during such channel conditions as result in optimum performance of the equalizer. Still further there is a need to implement an equalizer in parallel with a RAKE receiver, wherein the equalizer only operates during specified operating conditions.